Staging: line6 driver.c: factorize code and cleanups

- Factorize the code from line6_send_raw_message and line6_send_program into line6_send
- Minor style cleanups

Signed-off-by: Frederik Deweerdt <frederik.deweerdt@xprog.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>